Selection of piping system is an important aspect of system design in any energy consuming system.
The selection issues such as material of pipe, configuration, diameter, insulation etc have their own
impact on the overall energy consumption of the system. Piping is one of those few systems when
you oversize, you will generally save energy; unlike for a motor or a pump.

Piping system design in large industrial complexes like Refineries, Petrochemicals, Fertilizer Plants
etc are done now a day with the help of design software, which permits us to try out numerous
possibilities. It is the relatively small and medium users who generally do not have access to design
tools use various rules of thumbs for selecting size of pipes in industrial plants. These methods of
piping design are based on either “worked before” or “educated estimates”. Since everything we do is
based on sound economic principles to reduce cost, some of the piping design thumb rules are also
subject to modification to suit the present day cost of piping hardware cost and energy cost. It is
important to remember that there are no universal rules applicable in every situation. They are to be
developed for different scenarios.

For example, a water piping system having 1 km length pumping water from a river bed pumping
station to a plant will have different set of rules compared to a water piping system having 5 meter
length for supplying water from a main header to a reactor. Hence the issue of pipe size i.e. diameter,
selection should be based on reducing the overall cost of owning and operating the system.

This guidebook covers the best practices in piping systems with a primary view of reducing energy
cost, keeping in mind the safety and reliability issues. The basic elements of best practice in piping
systems are:

Density: This is the mass per unit volume of the fluid and is generally measured in kg/m3. Another
commonly used term is specific gravity. This is in fact a relative density, comparing the density of a
fluid at a given temperature to that of water at the same temperature.

Viscosity: This describes the ease with which a fluid flows. A substance like treacle has a high
viscosity, while water has a much lower value. Gases, such as air, have a still lower viscosity. The
viscosity of a fluid can be described in two ways.

• Kinematic viscosity: This is the ratio of the absolute viscosity to the density and is measured
in metres squared per second (m
2
/s).

Reynolds Number: A useful factor in determining which type of flow is involved is the Reynolds
number. This is the ratio of the dynamic forces of mass flow to the shear resistance due to fluid
viscosity and is given by the following formula. In general for a fluid like water when the Reynolds
number is less than 2000 the flow is laminar. The flow is turbulent for Reynolds numbers above 4000.
In between these two values (2000<Re<4000) the flow is a mixture of the two types and it is difficult
to predict the behavior of the fluid.
µ
ρ
×
× ×
=
1000
d u
Re
Where:
ρ = Density (kg/m
3
)
u = Mean velocity in the pipe (m/s)
d = Internal pipe diameter (mm)
µ = Dynamic viscosity (Pa s)

2.2 Types of Fluid Flow:

When a fluid moves through a pipe two distinct types of flow are possible, laminar and turbulent.

Laminar flow occurs in fluids moving with small average velocities and turbulent flow becomes
apparent as the velocity is increased above a critical velocity. In laminar flow the fluid particles move
along the length of the pipe in a very orderly fashion, with little or no sideways motion across the
width of the pipe.

Turbulent flow is characterised by random, disorganised motion of the particles, from side to side
across the pipe as well as along its length. There will, however, always be a layer of laminar flow at
the pipe wall - the so-called 'boundary layer'. The two types of fluid flow are described by different
sets of equations. In general, for most practical situations, the flow will be turbulent.

6
2.3 Pressure Loss in Pipes

Whenever fluid flows in a pipe there will be some loss of pressure due to several factors:

a) Friction: This is affected by the roughness of the inside surface of the pipe, the pipe diameter,
and the physical properties of the fluid.

b) Changes in size and shape or direction of flow

a) Obstructions: For normal, cylindrical straight pipes the major cause of pressure loss will be
friction. Pressure loss in a fitting or valve is greater than in a straight pipe. When fluid flows in a
straight pipe the flow pattern will be the same through out the pipe. In a valve or fitting changes
in the flow pattern due to factors (b) and (c) will cause extra pressure drops. Pressure drops
can be measured in a number of ways. The SI unit of pressure is the Pascal. However pressure
is often measured in bar.
This is illustrated by the D’Arcy equation:
gd
fLu
hf
2
2
=
Where:
L = Length (m)
u = Flow velocity (m/s)
g = Gravitational constant (9.81 m/s²)
d = Pipe inside diameter (m)
h
f
= Head loss to friction (m)
f = Friction factor (dimensionless)

Before the pipe losses can be established, the friction factor must be calculated. The friction factor
will be dependant on the pipe size, inner roughness of the pipe, flow velocity and fluid viscosity. The
flow condition, whether ‘Turbulent’ or not, will determine the method used to calculate the friction
factor.

Fig 2.1 can be used to estimate friction factor. Roughness of pipe is required for friction factor
estimation. The chart shows the relationship between Reynolds number and pipe friction. Calculation
of friction factors is dependant on the type of flow that will be encountered. For Re numbers <2320
the fluid flow is laminar, when Re number is >= 2320 the fluid flow is turbulent.

The following table gives typical values of absolute roughness of pipes, k. The relative roughness k/d
can be calculated from k and inside diameter of pipe.
7
Figure 2-1: Estimation of friction factor
The absolute roughness of pipes is given below.

A sample calculation of pressure drop is given below.

A pipe of 4” Dia carrying water flow of 50 m
3
/h through a distance of 100 metres. The pipe material is
Cast Iron with absolute roughness of 0.26.

2.4 Standard Pipe dimensions
There are a number of piping standards in existence around the world, but arguably the most global
are those derived by the American Petroleum Institute (API), where pipes are categorised in
schedule numbers. These schedule numbers bear a relation to the pressure rating of the piping.
There are eleven Schedules ranging from the lowest at 5 through 10, 20, 30, 40, 60, 80, 100, 120,
140 to schedule No. 160. For nominal size piping 150 mm and smaller, Schedule 40 (sometimes
called ‘standard weight’) is the lightest that would be specified for water, compressed air and steam
applications. High-pressure compressed air will have schedule 80 piping.
Regardless of schedule number, pipes of a particular size all have the same outside diameter (not
withstanding manufacturing tolerances). As the schedule number increases, the wall thickness
increases, and the actual bore is reduced. For example:
• A 100 mm Schedule 40 pipe has an outside diameter of 114.30 mm, a wall
thickness of 6.02 mm, giving a bore of 102.26 mm.
• A 100 mm Schedule 80 pipe has an outside diameter of 114.30 mm, a wall
thickness of 8.56 mm, giving a bore of 97.18 mm.
2.5 Pressure drop in components in pipe systems
Minor head loss in pipe systems can be expressed as:
9
h
minor_loss
=
g
ku
2
2

where h
minor_loss
= minor head loss (m)
k = minor loss coefficient
u

= flow velocity (m/s)
g = acceleration of gravity (m/s
2
)

Minor loss coefficients for some of the most common used components in pipe and tube systems are
given in table 2.1.

The above equations and table can be used for calculating pressure drops and energy loss
associated in pipes and fittings.
2.6 Valves

Valves isolate, switch and control fluid flow in a piping system. Valves can be operated manually with
levers and gear operators or remotely with electric, pneumatic, electro-pneumatic, and electro-
hydraulic powered actuators. Manually operated valves are typically used where operation is
infrequent and/or a power source is not available. Powered actuators allow valves to be operated
automatically by a control system and remotely with push button stations. Valve automation brings
significant advantages to a plant in the areas of process quality, efficiency, safety, and productivity.
10

Types of valves and their features are summarised below.
• Gate Valves have a sliding disc (gate) that reciprocates into and out of the valve port. Gate
valves are an ideal isolation valve for high pressure drop and high temperature applications
where operation is infrequent. Manual operation is accomplished through a multi turn hand
wheel gear shaft assembly. Multiturn electric actuators are typically required to automate gate
valves, however long stroke pneumatic and electro-hydraulic actuators are also available.

Applications: Oil, gas, air, slurries, heavy liquids, steam, non-condensing gases, and corrosive
liquids
Advantages: Disadvantages:
1. High capacity 1. Poor control
2. Tight shutoff 2. Cavitate at low pressure drops
3. Low cost 3. Cannot be used for throttling
4. Little resistance to flow
• Globe Valves have a conical plug, which reciprocates into and out of the valve port. Globe
valves are ideal for shutoff as well as throttling service in high pressure drop and high
temperature applications. Available in globe, angle, and y-pattern designs. Manual operation is
accomplished through a multi-turn hand wheel assembly. Multiturn electric actuators are
typically required to automate globe valves, however linear stroke pneumatic and electro-
hydraulic actuators are also available.

11

Recommended Uses:
1. Throttling service/flow regulation
2. Frequent operation
Applications: Liquids, vapors, gases, corrosive substances, slurries
Advantages: Disadvantages:
1. Efficient throttling 1. High pressure drop
2. Accurate flow control 2. More expensive than other valves
3. Available in multiple ports
o Ball Valves were a welcomed relief to the process industry. They provide tight shutoff and high
capacity with just a quarter-turn to operate. Ball valves are now more common in 1/4"-6" sizes.
Ball valves can be easily actuated with pneumatic and electric actuators.

Recommended Uses:
1. Fully open/closed, limited-throttling
2. Higher temperature fluids
Applications: Most liquids, high temperatures, slurries
Advantages: Disadvantages:
1. Low cost 1. Poor throttling characteristics
2. High capacity 2. Prone to cavitation
3. Low leakage and maint.
4. Tight sealing with low torque
Butterfly valves are commonly used as control valves in applications where the pressure drops
required of the valves are relatively low. Butterfly valves can be used in applications as either shutoff
valves (on/off service) or as throttling valves (for flow or pressure control). As shutoff valves, butterfly
valves offer excellent performance within the range of their pressure rating.
12
Typical uses would include isolation of equipment, fill/drain systems, and bypass systems and other
like applications where the only criterion for control of the flow/pressure is that it be on or off. Although
butterfly valves have only a limited ability to control pressure or flow, they have been widely used as
control valves because of the economics involved. The control capabilities of a butterfly valve can
also be significantly improved by coupling it with an operator and electronic control package.

3.1 Introduction
The purpose of the compressed air piping system is to deliver compressed air to the points of usage.
The compressed air needs to be delivered with enough volume, appropriate quality, and pressure to
properly power the components that use the compressed air. Compressed air is costly to
manufacture. A poorly designed compressed air system can increase energy costs, promote
equipment failure, reduce production efficiencies, and increase maintenance requirements. It is
generally considered true that any additional costs spent improving the compressed air piping system
will pay for them many times over the life of the system.

3.2 Piping materials
Common piping materials used in a compressed air system include copper, aluminum, stainless steel
and carbon steel. Compressed air piping systems that are 2" or smaller utilize copper, aluminum or
stainless steel. Pipe and fitting connections are typically threaded. Piping systems that are 4" or larger
utilize carbon or stainless steel with flanged pipe and fittings. Plastic piping may be used on
compressed air systems, however caution must used since many plastic materials are not compatible
with all compressor lubricants. Ultraviolet light (sun light) may also reduce the useful service life of
some plastic materials. Installation must follow the manufacturer's instructions.

Corrosion-resistant piping should be used with any compressed air piping system using oil-free
compressors. A non-lubricated system will experience corrosion from the moisture in the warm air,
contaminating products and control systems, if this type of piping is not used.

It is always better to oversize the compressed air piping system you choose to install. This reduces
pressure drop, which will pay for itself, and it allows for expansion of the system.

3.3 Compressor Discharge Piping
The discharge piping from the compressor should be at least as large as compressor discharge
connection and it should run directly to the after cooler. Discharge piping from a compressor without
an integral after cooler can have very high temperatures. The pipe that is installed here must be able
to handle these temperatures. The high temperatures can also cause thermal expansion of the pipe,
which can add stress to the pipe. Check the compressor manufacturer's recommendations on
discharge piping. Install a liquid filled pressure gauge, a thermometer, and a thermowell in the
discharge airline before the aftercooler. Proper support and/or flexible discharge pipe can eliminate
strain.

1. The main header pipe in the system should be sloped downward in the direction of the
compressed air flow. A general rule of thumb is 1" per 10 feet of pipe. The reason for the slope
is to direct the condensation to a low point in the compressed air piping system where it can be
collected and removed.
2. Make sure that the piping following the after cooler slopes downward into the bottom
connection of the air receiver. This helps with the condensate drainage, as well as if the water-
cooled after cooler develops a water leak internally. It would drain toward the receiver and not
the compressor.
3. Normally, the velocity of compressed air should not be allowed to exceed 6 m/s; lower
velocities are recommended for long lines. Higher air velocities (up to 20 m/s) are acceptable
where the distribution pipe-work does not exceed 8 meters in length. This would be the case
where dedicated compressors are installed near to an associated large end user.
14
4. The air distribution should be designed with liberal pipe sizes so that the frictional pressure
losses are very low; larger pipe sizes also help in facilitating system expansion at a later stage
without changing header sizes or laying parallel headers.

3.4 Pressure Drop
Pressure drop in a compressed air system is a critical factor. Pressure drop is caused by friction of
the compressed air flowing against the inside of the pipe and through valves, tees, elbows and other
components that make up a complete compressed air piping system. Pressure drop can be affected
by pipe size, type of pipes used, the number and type of valves, couplings, and bends in the system.
Each header or main should be furnished with outlets as close as possible to the point of application.
This avoids significant pressure drops through the hose and allows shorter hose lengths to be used.
To avoid carryover of condensed moisture to tools, outlets should be taken from the top of the
pipeline. Larger pipe sizes, shorter pipe and hose lengths, smooth wall pipe, long radius swept tees,
and long radius elbows all help reduce pressure drop within a compressed air piping system.

The discharge pressure of the compressor is determined by the maximum pressure loss plus
operating pressure value so that air is delivered at right pressure to the farthest equipment. For
example, a 90 psig air grinder installed in the farthest drop from the compressor may require 92 psig
in the branch line 93 psig in the sub-header and 94 psig at the main header. With a 6 psi drop in the
filter/dryer, the discharge pressure at the after cooler should be 100 psig.

The following nomogram can be used to estimate pressure drop in a compressed air system. Draw a
straight line starting at pipe internal diameter and through flow (m/s) to be extended to the reference
line. From this point draw another line to meet the air pressure (bar) line. The point of intersection of
this line with the pressure drop line gives the pressure drop in mbar/m.

15

Figure 3-1: Pressure drop calculations

3.5 Piping system Design
There are two basic systems for distribution system.

1. A single line from the supply to the point(s) of usage, also known as radial system

2. Ring main system, where supply to the end use is taken from a closed loop header. The loop
design allows airflow in two directions to a point of use. This can cut the overall pipe length to
a point in half that reduces pressure drop. It also means that a large volume user of
compressed air in a system may not starve users downstream since they can draw air from
another direction. In many cases a balance line is also recommended which provides another
source of air. Reducing the velocity of the airflow through the compressed air piping system is
another benefit of the loop design. This reduces the velocity, which reduces the friction
against the pipe walls and reduces pressure drop.

16

Figure 3-2: Types o piping layout
3.6 Compressed Air leakage
Leaks can be a significant source of wasted energy in an industrial compressed air system and may
be costing you much more than you think. Audits typically find that leaks can be responsible for
between 20-50% of a compressor’s output making them the largest single waste of energy. In
addition to being a source of wasted energy, leaks can also contribute to other operating losses:

• Leaks cause a drop in system pressure. This can decrease the efficiency of air tools
and adversely affect production
• Leaks can force the equipment to cycle more frequently, shortening the life of almost all
system equipment (including the compressor package itself)
• Leaks can increase running time that can lead to additional maintenance requirements
and increased unscheduled downtime
• Leaks can lead to adding unnecessary compressor capacity
Observing the average compressor loading and unloading time, when there is no legitimate use of
compressed air on the shop floor, can estimate the leakage level. In continuous process plants, this test
can be conducted during the shutdown or during unexpected production stoppages.
Air Leakage = On load time
Q x --------------------------------------
On load time + Off load time

Where Q = compressor capacity
17
3.7 Leakage reduction

Leakage tests can be conducted easily, but identifying leakage points and plugging them is laborious
work; obvious leakage points can be identified from audible sound; for small leakage, ultrasonic
leakage detectors can be used; soap solution can also be used to detect small leakage in accessible
lines.

FITTINGS AND FLANGES - Check joints and supports are adequate. Check for twisting.

MANIFOLDS - Check for worn connectors and poorly jointed pipe work.

FLEXIBLE HOSES - Check that the hose is moving freely and clear of abrasive surfaces. Check for
deterioration and that the hose has a suitable coating for the environment e.g. oily conditions. Is the
hose damaged due to being too long or too short?

FILTERS Check drainage points and contaminated bowls.
TOOLS Check hose connections and speed control valve. Check air tools are always switched off
when not in use.

The following points can help reduce compressed air leakage:

• Reduce the line pressure to the minimum acceptable; this can be done by reducing the discharge
pressure settings or by use of pressure regulators on major branch lines.
• Selection of good quality pipe fittings.
• Provide welded joints in place of threaded joints.
• Sealing of unused branch lines or tapings.
• Provide ball valves (for isolation) at the main branches at accessible points, so that these can be
closed when air is not required in the entire section. Similarly, ball valves may be provided at all end
use points for firm closure when pneumatic equipment is not in use.
• Install flow meters on major lines; abnormal increase in airflow may be an indicator of increased
leakage or wastage.
• Avoid installation of underground pipelines; pipelines should be overhead or in trenches (which can
be opened for inspection). Corroded underground lines can be a major source of leakage.
18
The following table 3.1 shows cost of compressed air leakage from holes at different pressures. It may be
noted that, at 7 bar (100 psig), about 100 cfm air leakage is equivalent to a power loss of 17 kW i.e. about
Rs.6.12 lakhs per annum.
Table 3-1: Cost of Compressed Air Leakage
Orifice
Diamete
r
Air
leakage
Scfm
Power
wasted
KW
Cost of Wastage (for 8000
hrs/year)
(@ Rs. 4.50/kWh
At 3 bar (45 psig) pressure
1/32” 0.845 0.109 3924
1/16” 3.38 0.439 15804
1/8” 13.5 1.755 63180
¼” 54.1 7.03 253080
At 4 bar (60 psig) pressure
1/32” 1.06 0.018 6487
1/16” 4.23 0.719 25887
1/8” 16.9 3.23 103428
¼” 164.6 14.57 395352
At 5.5 bar (80 psig) pressure
1/32” 1.34 0.228 8201
1/16” 5.36 0.911 32803
1/8” 21.4 3.64 130968
¼” 85.7 14.57 524484
At 7 bar (100 psig) pressure
1/32” 1.62 0.275 9915
1/16” 6.49 1.10 39719
1/8” 26 4.42 159120
¼” 104 17.68 636480
19

4 STEAM DISTRIBUTION

4.1 Introduction
The objective of the steam distribution system is to supply steam at the correct pressure to the point
of use. It follows; therefore, that pressure drop through the distribution system is an important feature.
One of the most important decisions in the design of a steam system is the selection of the
generating, distribution, and utilization pressures. Considering investment cost, energy efficiency, and
control stability, the pressure shall be held to the minimum values above atmospheric pressure that
are practical to accomplish the required heating task, unless detailed economic analysis indicates
advantages in higher pressure generation and distribution.
The piping system distributes the steam, returns the condensate, and removes air and non-
condensable gases. In steam heating systems, it is important that the piping system distribute steam,
not only at full design load, but also at partial loads and excess loads that can occur on system warm-
up. When the system is warming up, the load on the steam mains and returns can exceed the
maximum operating load for the coldest design day, even in moderate weather. This load comes from
raising the temperature of the piping to the steam temperature and the building to the indoor design
temperature.

4.2 Energy Considerations
Steam and condensate piping system have a great impact on energy usage. Proper sizing of system
components such as traps, control valves, and pipes has a tremendous effect on the efficiencies of
the system.

Condensate is a by-product of a steam system and must always be removed from the system as
soon as it accumulates, because steam moves rapidly in mains and supply piping, and if condensate
accumulates to the point where the steam can push a slug of it, serious damage can occur from the
resulting water hammer. Pipe insulation also has a tremendous effect on system energy efficiency. All
steam and condensate piping should be insulated. It may also be economically wise to save the
sensible heat of the condensate for boiler water make-up systems operational efficiency

Oversized pipe work means:
• Pipes, valves, fittings, etc. will be more expensive than necessary.
• Higher installation costs will be incurred, including support work, insulation, etc.
• For steam pipes a greater volume of condensate will be formed due to the greater heat loss.
This, in turn, means that either:
• More steam trapping is required, or wet steam is delivered to the point of use.
In a particular example:
• The cost of installing 80 mm steam pipe work was found to be 44% higher than the cost of 50
mm pipe work, which would have had adequate capacity.
20
• The heat lost by the insulated pipe work was some 21% higher from the 80 mm pipeline than it
would have been from the 50 mm pipe work. Any non-insulated parts of the 80 mm pipe would
lose 50% more heat than the 50 mm pipe, due to the extra heat transfer surface area.
Undersized pipe work means:
• A lower pressure may only be available at the point of use. This may hinder equipment
performance due to only lower pressure steam being available.
• There is a risk of steam starvation.
• There is a greater risk of erosion, water hammer and noise due to the inherent increase in steam
velocity.
The allowance for pipe fittings:
The length of travel from the boiler to the unit heater is known, but an allowance must be included
for the additional frictional resistance of the fittings. This is generally expressed in terms of
‘equivalent pipe length’. If the size of the pipe is known, the resistance of the fittings can be
calculated. As the pipe size is not yet known in this example, an addition to the equivalent length can
be used based on experience.
• If the pipe is less than 50 metres long, add an allowance for fittings of 5%.
• If the pipe is over 100 metres long and is a fairly straight run with few fittings, an allowance for
fittings of 10% would be made.
• A similar pipe length, but with more fittings, would increase the allowance towards 20%.
4.3 Selection of pipe size

There are numerous graphs, tables and slide rules available for relating steam pipe sizes to flow
rates and pressure drops.

To begin the process of determining required pipe size, it is usual to assume a velocity of flow. For
saturated steam from a boiler, 20 - 30 m/s is accepted general practice for short pipe runs. For major
lengths of distribution pipe work, pressure drop becomes the major consideration and velocities may
be slightly less. With dry steam, velocities of 40 metres/sec can be contemplated -but remember that
many steam meters suffer wear and tear under such conditions. There is also a risk of noise from
pipes.
Draw a horizontal line from the saturation temperature line (Point A) on the pressure scale to the
steam mass flow rate (Point B).
• From point B, draw a vertical line to the steam velocity of 25 m/s (Point C). From point C, draw a
horizontal line across the pipe diameter scale (Point D).

21

Figure 4-1: Steam pipe sizing
The following table also summarises the recommended pipe sizes for steam at various pressure and
mass flow rate.

1. All underground steam systems shall be installed a minimum of 10 feet from plastic piping and
chilled water systems. All plastic underground piping must be kept at a 10 foot distance from
steam/condensate lines.
2. Install piping free of sags or bends and with ample space between piping to permit proper
insulation applications.
3. Install steam supply piping at a minimum, uniform grade of 1/4 inch in 10 feet downward in the
direction of flow.
4. Install condensate return piping sloped downward in the direction of steam supply. Provide
condensate return pump at the building to discharge condensate back to the Campus collection
system.
5. Install drip legs at intervals not exceeding 200 feet where pipe is pitched down in the direction
of the steam flow. Size drip legs at vertical risers full size and extend beyond the rise. Size drip
legs at other locations same diameter as the main. Provide an 18-inch drip leg for steam mains
smaller than 6 inches. In steam mains 6 inches and larger, provide drip legs sized 2 pipe sizes
smaller than the main, but not less than 4 inches.
6. Drip legs, dirt pockets, and strainer blow downs shall be equipped with gate valves to allow
removal of dirt and scale.
7. Install steam traps close to drip legs.

Size of pipe line (diameter) mm 50 75 150
Pressure drop in pipe line/metre m 0.1690 0.0235 0.0008
Length of cooling water pipe line m 100.0 100.0 100.0
Equivalent pipe length for 10 nos. bends m 15.0 22.5 45.0
Equivalent pipe length for 4 nos. valves m 2.6 3.9 7.8
Total equivalent length of pipe m 117.6 126.4 152.8
Total frictional head loss in pipes/fittings m 19.9 3.0 0.1
Pressure drop across heat exchanger, assumed m 5 5 5
Static head requirement, assumed m 5 5 5
Total head required by the pump m 29.9 13.0 10.1
Likely motor input power kW 2.2 1.0 0.9
If a 2” pipe were used, the power consumption would have been more than double compared to the
3” pipe. Looking at the velocities, it should be noted that for smaller pipelines, lower design velocities
25
are recommended. For a 12” pipe, the velocity can be 2.6 m/s without any or notable energy penalty,
but for a 2” to 6” line this can be very lossy.
To avoid pressure losses in these systems:
1. First, decide the flow
2. Calculate the pressure drops for different pipe sizes and estimate total head and
power requirement
3. Finally, select the pump.
5.2 Recommended water flow velocity on suction side of pump
Capacity problems, cavitation and high power consumption in a pump, is often the result of the
conditions on the suction side. In general - a rule of thumb - is to keep the suction fluid flow speed
below the following values:

6.1 Introduction
There are many reasons for insulating a pipeline, most important being the energy cost of not
insulating the pipe. Adequate thermal insulation is essential for preventing both heat loss from hot
surfaces of ovens/furnaces/piping and heat gain in refrigeration systems. Inadequate thickness of
insulation or deterioration of existing insulation can have a significant impact on the energy
consumption. The material of insulation is also important to achieve low thermal conductivity and
also low thermal inertia. Development of superior insulating materials and their availability at
reasonable prices have made retrofitting or re-insulation a very attractive energy saving option.
The simplest method of analysing whether you should use 1” or 2” or 3” insulation is by comparing
the cost of energy losses with the cost of insulating the pipe. The insulation thickness for which the
total cost is minimum is termed as economic thickness. Refer fig 6.1. The curve representing the total
cost reduces initially and after reaching the economic thickness corresponding to the minimum cost, it
increases.

Figure 6-1: Economic insulation thickness
However, in plants, there are some limitations for using the results of economic thickness
calculations. Due to space limitations, it is sometimes not possible to accommodate larger diameter of
insulated pipes.
A detailed calculation on economic thickness is given in section 6.5.

27
6.2 Heat Losses from Pipe surfaces
Heat loss from 1/2" to 12" steel pipes at various temperature differences between pipe and air can be
found in the table below.
Table 6-1: Heat loss from Fluid inside Pipe (W/m)

From the above equation, and for a desired T
s
, R
l
can be calculated. From R
l
and known value of
thermal conductivity k, thickness of insulation can be calculated.
Equivalent thickness of insulation for pipe, E
tk
.=
( )
|
¹
|

\
| +
× +
1
k 1
k 1
r
t r
ln ) t (r

6.4 Insulation material
Insulation materials are classified into organic and inorganic types. Organic insulations are based on
hydrocarbon polymers, which can be expanded to obtain high void structures. Examples are
thermocol (Expanded Polystyrene) and Poly Urethane Form (PUF). Inorganic insulation is based on
Siliceous/Aluminous/Calcium materials in fibrous, granular or powder forms. Examples are Mineral
wool, Calcium silicate etc.

Properties of common insulating materials are as under:

Calcium Silicate: Used in industrial process plant piping where high service temperature and
compressive strength are needed. Temperature ranges varies from 40 C to 950 C.

Glass mineral wool: These are available in flexible forms, rigid slabs and preformed pipe work
sections. Good for thermal and acoustic insulation for heating and chilling system pipelines.
Temperature range of application is –10 to 500 C

Thermocol: These are mainly used as cold insulation for piping and cold storage construction.

Expanded nitrile rubber: This is a flexible material that forms a closed cell integral vapour barrier.
Originally developed for condensation control in refrigeration pipe work and chilled water lines; now-a-
days also used for ducting insulation for air conditioning.

Rock mineral wool: This is available in a range of forms from light weight rolled products to heavy
rigid slabs including preformed pipe sections. In addition to good thermal insulation properties, it can
also provide acoustic insulation and is fire retardant.

The thermal conductivity of a material is the heat loss per unit area per unit insulation thickness per
unit temperature difference. The unit of measurement is W-m
2
/m°C or W-m/°C. The thermal
conductivity of materials increases with temperature. So thermal conductivity is always specified at
the mean temperature (mean of hot and cold face temperatures) of the insulation material.

Thermal conductivities of typical hot and cold insulation materials are given below.

Refer table 6.3. Insulation thickness is given in mm for refrigeration systems with fluid temperatures
varying from 10 to –20° C is given below. The emissivity of surface (typically cement, gypsum etc) is
high at about 0.9. Ambient temperature is 25° C and 80% RH.

6.6 Economic thickness of insulation
To explain the concept of economic thickness of insulation, we will use an example. Consider an 8
bar steam pipeline of 6” dia having 50-meter length. We will evaluate the cost of energy losses when
we use 1”, 2” and 3” insulation to find out the most economic thickness.

Note that the total cost in lower when using 2” insulation, hence is the economic insulation thickness.

34

7 CASE STUDIES

7.1 Pressure drop reduction in water pumping

The Pharmaceutical plant had a 4” pipeline main header for distributing chilled water from the chilling
plant to the end uses. The number of end uses of chilled water has increased over the years;
however, the main header size remained the same at 4”.

Figure 7-1: Chilled water system piping schematic

Flow measured was varying from 120 to 180 m3/h. It was observed that the line pressure at the main
header at the inlet to plant-2 was 2.2 bars only when the pump discharge pressure was 4.7 bars. At
plat-6, the line pressure was 2.0 bar. The pressure drop was about 2.5 bar!

It was clear that the pressure drop in the main header section having 22 meter length ( refer figure
above) was very high. Usually, a 4” line is used for carrying a maximum flow of 60 m3/hr and for very
short distances, it can carry 80 m3/h. The pump power consumption was 35 kW.

Modifications:

An additional 4” line was laid parallel to the main header up to plant –7 supply point. The existing
pressure drop of 2.5 bar reduced to 0.5 bar. Along with this, the existing pump impeller was trimmed
properly so that the new discharge pressure was 3.0 bar. The power consumption after modification
was 21.0 kW.

35
Power saving of 14 kW has resulted by this measure. Annual energy saving was 1,12,000 kWh. I.e.
Rs 4.8 lakhs/annum. Investment for the piping modifications was Rs 80,000/- with a payback period
of 2 months.

7.2 Pressure drop reduction in Compressed air system

In this synthetic yarn manufacturing plant, compressed air is generated at 12 bar for supplying air to
FDY plant. The central compressor station located at about 250 metres from the FDY plant consists
of reciprocating compressors, dryers, receivers etc. The average airflow requirement is 760 Nm3/h.
Compressed air to some other plants are also supplied from the same station. These sections,
though supplied by 12 bar compressed air use air at 8.0 bar. The total compressed air generation at
12 bar was 3800 Nm3/h.

For satisfactory operation of FDY machines, the pressure required at the machine is 9.0 bar. Refer
fig 4.2. There were 2 rows of FDY machines, one consisting of old FDY machines and the other
having new machines in large numbers. Originally, the old FDY machines were supplied air through a
2” line from the compressor. For the new FDY machines, a 6” header was installed. The 2” and 6”
lines were independently operated, and there was no interconnection between them.

During a pressure optimisation study, it was seen that the air pressure at old FDY machines was 9.5
bar; at the same time pressure at new FDY machines was 11.0 bar. While investigating the reasons
for the difference in pressure it was found that due to small size of old FDY header, the pressure drop
was significant.

Figure 7-2: Compressed air system piping schematic

Modification:

It was decided to interconnect the 2” and 6” line near the FDY plant so that the air requirement at
FDY plant is shared by both lines and hence less pressure drop in the 2” line. Measurements after the
modifications indicated that the pressure at old FDY machines were 10.5 bar when the supply
pressure was 12 bar.

Interestingly, the 2.5 bar pressure drop in the 2” line was the sole reason for keeping the air pressure
at a higher margin. The pressure setting for the entire station was reduced to 10.5 bar after the
modification. I.e a reduction of 1.5 bar. The total power consumption of 500 kW for 3800 Nm3/h
reduced to 455 kW after the modifications. Minor piping cost was incurred for the modifications.
Annual saving was 3,60,000 kWh/annum. I.e Rs 8.0 lakhs per annum.

7.3 Replacement of Globe Valves with Butterfly Valves
An often overlooked opportunity to reduce waste energy-particularly during retrofit applications-is the
type of throttling valve used. The ISA handbook of control valves states that "In a pumped circuit, the
36
pressure drop allocated to the control valve should be equal to 33% of the dynamic loss in the system
at the rated flow, or 15 psi, whichever is greater."
An inherent result of this guideline is that high-loss valves, such as globe valves, are frequently used
for control purposes. These valves result in significant losses even when they are full open. Figure
4.3 illustrates the frictional head loss for three styles of full-open 12-inch valves as a function of flow
rate. (The "K" value is the valve loss coefficient at full-open position.). Even at relatively low flow
rates, the power losses can be significant in high-loss valves. For instance, at 1500 gpm (for which
the fluid velocity in a 12-inch line is only about 4.3 ft/sec), about 3.3 hp is lost to valve friction in the
reduced trim globe valve.
Assuming the combined pump and motor efficiency is 70%, the cost of electricity is 10¢/kWh, and
continuous system operation, the annual cost of friction can be estimated. About $ 3000/annum is
saved by replacing the globe valve with k=30 by a butterfly valve of k=0.35.
A 250-lb pressure class butterfly valve can be purchased and installed for less than $1,000. The
simple return on investment period would range from only 4 months to a year at 1500 gpm flow.

Figure 7-3: Pressure drop of Globe & Butterfly Valves
7.4 Reduction in pressure drop in the compressed air network
A leading bulk drug company has three reciprocating compressors located in a centralized
compressor house. During the normal operation only one compressor is operated. The peak
compressed air consumption in the plant is about 280 cfm and the corresponding power consumption
was 58 kW (4.83 cfm /kW @ 7.5 kg/cm2). The pressure requirement at the user end was only 6
kg/cm2.

The compressor main line size is of is 2” inch. The main line air pressure near the receiver located
next to the compressor house varies from 6.8 – 8 kg/cm2g. Pressure drop survey was carried out to
evaluate the distribution system. The survey revealed that pressure drop in the system is as high as
1.5 kg/cm2g. The pressure drop in the distribution network (from the compressor house to entry to the
user divisions) should not have been more than 0.6 kg/cm2, whereas in this case, the pressure drop
37
is much higher than the optimum values. High pressure drop in the system was due to under
sizing of the piping.

Moreover, at lower pressures and high volume flow rates, the air velocity and pressure drop is quite
high. In order to maintain the required pressure at user ends, the generating air pressure was always
kept higher than the compressor rated pressure of 7.03 kg/cm2. Maintaining higher generating
pressure than rated, results in higher power consumption at the compressor and increased stress on
the compressor leading to heating of the machine. The latter can be sensed by difference in water
temperatures across the inter and after coolers.

Suggestion:
Existing pipe was replaced with 3” line reduced pressure drop by 1.0-1.5 kg/cm2. There by the
generating pressure settings were reduced to 6.0- 6.5 kg/cm2g.

7.5 Thermal insulation in Steam distribution system
A leading pharmaceutical company has one 4 tph boiler to meet the steam requirement of the plant.
The boiler uses furnace oil and consumes about 900 kL of furnace oil per year, which accounts for
about Rs. 60 Lakh. The steam generation pressure at the common header varied from 7-9 kg/cm2-g.
Steam is supplied to various sections of the plant. Detailed survey indicated that the insulation of the
steam lines was completely damaged. The surface temperatures measured in the range of 68-80 oC,
which were on higher side. The steam insulation was damaged from the top and it was also observed
that the water was entrapped in the insulation and causing huge steam losses.

Estimated surface heat losses indicated that about 16-17 lph of furnace oil was consumed to
compensate the losses. Plant has taken immediate measure to replace the entire insulation and
replaced with 2-3” of insulation

This large engineering plant manufactures boilers and other heat exchangers. Use of compressed air
was extensive for a number of machines and pneumatic tools. The overall housekeeping of the plant
was very good; a walk through of the plant on a holiday with compressor distribution energised was
done and very few leakages were seen at the end uses.

38
The compressed air leakage was observed to be extremely low, keeping in view the vastness of the
plant where production activities are spread over a dozen bays. The leakage levels were very low in
all bays (in the range of 6 to 33 cfm), except in the case bays nos. 5 and 5A, where it was as high as
196 cfm. Inspection of the plant pipeline, joints and end use points showed virtually no leakage. This
was surprising because a leakage of 196 cfm would generally create sufficient hissing sounds to help
in its detection.

Then it was conjectured that the leakage was possibly in the main header from the compressor room
to the bays, which has a short run underground. Since part of the main header was buried in the
foundation of a large machine, we presumed that the sound of leakage was being muffled. Inspection
of the foundation showed mild drafts of air leaking from some crevices. Though there was no
conclusive proof, a decision was taken to replace the short underground line with an overhead line.

The leakage test after the replacement of the line clearly indicated that the leakage had dropped from
196 cfm to about 15 cfm. The estimated energy savings are 1,80,000 kWh/annum i.e. Rs 5.4
lacs/annum.

The investment for replacing the compressed air line was Rs.30,000/-. It may be noted that the
investment was paid back in only 21 days.

7.7 Reducing Steam Header Pressure
EDFORD
In any steam system, reducing unnecessary steam flow will reduce energy consumption and, in many
cases, lower overall operating costs. This flow reduction can be achieved in many steam systems by
lowering normal operating pressure in the steam header. To determine if such a cost saving
opportunity is feasible, industrial facilities should evaluate the end use requirements of their steam
system.

By evaluating its steam system and end-use equipment, Nalco Chemicals, USA realized that a lower
header pressure could still meet system needs. The services performed by high-level steam jets were
no longer required for the products manufactured at this plant. Instead, the steam system only
needed to serve process heating and low-level steam jets, which require lower steam pressure.

The following benefits were expected from this measure.

• Decreased friction losses resulting from lower steam and condensate flow rates. Because the
head loss due to friction in a piping system is proportional to the square of the flow rate, a 20%
reduction in flow rates results in a 36% reduction in friction loss.

• Lower piping surface energy losses due to lower steam temperatures.

• Reduced steam losses from leaks.

• Less flash steam in the condensate recovery system, this reduces the chance of water hammer
and stress on the system.

To minimize the risk of unexpected problems, the steam header pressure was first reduced from 125
psig to 115 psig. Changes in system operating conditions should be implemented carefully to avoid
adverse affects on product quality. The participation of system operators is essential in both planning
the change and subsequently monitoring the effects on system performance. At Nalco, after no
problems were observed from the first reduction in header pressure, the pressure was stepped down
further to 100 psig. Encouraged by the success of their efforts, Nalco is evaluating the feasibility of
reducing the pressure even more.

39
Results
Overall, reducing steam header pressure was successful. This project did not require a capital
investment and minimal downtime was necessary. The only costs associated with this project were
for labor resources to analyze project feasibility, to recalibrate the flow meter (which receives periodic
calibration anyway), and to monitor system response to the operating change. Nalco realized annual
energy savings of 56,900 million Btu, cutting costs by $142,000 annually. On a per pound of product
basis, the amount of energy was reduced by 8%, from 2,035 Btu/lb to 1,873 Btu/lb. The decreased
fuel consumption translates into an annual 3,300-ton decrease in CO2 emissions. Additionally, by
operating at lower energy levels and flow velocities, the steam and condensate systems experience
less erosion and valve wear.

40
7.9 Cooling water piping system modification to increase productivity
The plant, located in Gujarat, manufactures benzene derivatives. Two cooling tower pumps operating
in parallel supply water to condensers in new hydrogenation plant. Specification of pumps is given
below.
Pump-1
Make: KSB, Model: MEGA G 32/180
Speed: 2900 rpm, Head: 32 m, Flow = 180 m3/h,
Efficiency : 81%
Motor: 30 HP, 2900 rpm
During the energy audit, measurements were taken on these pumps as summarised below.
Pump No.1 No.2
Power input, kW 17.9 17.7
Flow, m3/h 120 122
Head, mWC 38 38
Operating efficiency, % 82 82
The discharge pressure of the pumps was found to be 38 mWC( 3.8 kg/cm2). Observing the piping
and end use equipments, it was found that all the valves are fully open and the 8” header was
properly sized to handle a flow of 180 m3/h. The pressure drop across the heat exchanger was also
low, of the order of 0.5 kg/cm2. The reason for higher discharge pressure was still elusive. The
process which is capable of 7 using condensers at a time, had to be operated with only 3 condensers
on line at a time.
Further observations of pressure at various points in the system indicated that the NRV (non return
valve) at the pump discharge is jammed. Pressure before the NRV, same as the pump discharge
pressure, was 3.8 kg/cm2 and after the NRV were 2.0 kg/cm2. Hence it was decided to install new
valves.
After replacing the existing NRVs with new valve, the system flow increased to 180 m3/h per pump,
an increase of about 50% in flow. Power consumption of the pumps also increased to 22.5 kW each.
However, the increase in productivity has also been 50% more resulting in higher throughput.
Increased energy cost of 9.4 kW was equivalent to Rs 1.8 lakhs per year, where as the value of
increase in production was roughly 10 times ( Rs 20.0 lakhs per year).
7.10 Excessive pressure drop due to inadequate piping-chilled water system
The plant located in Ankleshwar, Gujarat manufactures Pesticides products. Chilling is a major end
use of energy, roughly about 15% the plant energy consumption. There are two ammonia based
vapour compression system to produce chilled water at 8 C. The specifications of the plant are as
follows.
Compressor make: Kirloskar
Model: KC6
Capacity ( at 0ºC SST) = 120 TR
Rated specific power consumption at above SST = 0.72 kW/TR
Rated primary flow = 61 m
3
/h
Rated condenser flow = 105 m
3
/h
The chilled water system has primary and secondary pumping arrangements. The primary pump
specifications and measurements are given below.
41

The pressure at pump discharge was 37.5 mWC and the pressure at chiller inlet was 28 mWC. This
indicated that the pressure drop in the 4” supply piping from pump to the chiller was 9.5 mWC. This is
very high. Similar pressure drop was observed in return line also.

The pipe sizing of 4” in generally adequate for a rated primary flow of 61 m3/h. However, due to
improper selection of pump, the pump is giving about 112.2 m3/h; almost double that of the required
flow rate. This flow through a 4: pipe is expected to produce a pressure drop of about 10 mWC.

The solution suggested was to reduce the primary flow, by reducing the impeller diameter. The plant
personnel wanted to know if reducing primary flow would effect the chilling capacity. A trial was taken
by reducing the flow by controlling valves to evaluate chiller performance. Flow reduced from 112
m
3
/h to 75 m
3
/h. Total reduction in pressure in the supply and return was 1.5 kg/cm2.

Figure 7-4: Chiller performance
Note that, with reduction in primary flow, inlet and outlet temperatures found to be reduced. Most
importantly, the capacity of the machine remained unaffected.
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After gaining confidence from the above exercise, the impeller diameter of primary pump was
reduced from existing 174 mm to 145 mm. Since the existing impeller diameter and the new impeller
diameter were very different, a new 145 mm impeller was purchased, instead of trimming.
After installing the new impeller, the performance is as follows.
Head: 23 mWC
Flow: 75 m
3
/h
Power input: 8.2 kW

Energy saving for 9 months,10 hours/day operation is found to be 15,660 kWh/annum. i.e. Rs
70,000/- per annum. Investment for a new impeller was Rs 4000/- with a payback period of one
month.